Selecting system



May 25, 1943.

N. l. HALL SELEGTING SYSTEM Patented May 25, 1943 SELEC'EENG SYSTEM( Nathan li. Halli, Morristown, N. 3., assigner to Bell Telephone Laboratories, Incorporated, New York, N. if., a corporation oi New York Application November 21, 1941, Serial No. 419,878

(Ci. 17d-i8) d Ciairns.

This invention relates to selecting systems and particularly to systems in which selections are made automatically in a group of lines, circuits, or other electrical devices.

,an object of the invention is to increase the certainty with which lines, trunks, circuits, orl other devices oi a group are rendered unselectabie in response to the selection or one of them for use.

Another object is to cause the selection of one of av plurality oi equivalent circuits lor devices by operatingV a discharge tube individual thereto and to utilize the characteristics of these discharge tubes to insure that one alone is rendered efiective and that all others are rendered ineffective when a plurality of them are seized simultaneously.

Another object is to utilize a common impedance element for controlling the operating voltages applied to said tubes and to utilize a source of alternating or pulsating voltage for varying the characteristics of the tubes to insure the ef iective operation of one tube to the exclusion of the other.

Other objects of theinvention are to simplify, to increase the speed of operation and otherwise to improve selecting and Controlling systems.

These objects are realized by means of a selecting system in which a plurality of lines, circuits, relays, or other equivalent devices, from which selection is to be made, are provided with a plurality of discharge tubes, one for each of the several circuits or devices, together with means forv causing the ionization or initial discharge of said tubes at random; in which the starting or ionizing voltage for each tube is applied through ajcommon impedance element; and in which a source of alternating or pulsating voltage is applied to the main discharge gaps of the tubes. In the practical operation of a selection system of this kind attempts to seize any two of the tubes, although subject to random occurrence, are more likely to fall in sequence than simultaneously. `And the first tube to ionize, although preceding only slightly an attempt to seize a second tube, will usually set up a suflicient voltage in the common impedance to lock out the second tube and all others as well. However, because the attempts do fall at random, it frequently happens that two or more tubes have their starting gaps ionized at substantially the same instant. But even'in these instances it would be highly undesirable to permit the failure that would result from double operation. In the present system such a failure is made practically speciiically the effect ci the alternat.

impossible by the combined eiect that is obtained by the use of the common impedance in ionizing circuits ci the tubes and the alternating or pulsating voltage on their main gaps. 'More lig voltage applied to the main gaps ci the tubes is to change the sustaining characteristics or" the tubes at dif ferent rates. Since the sustaining voltage of the starting gap of a particular one of a plurality of simultaneously ionized tubes is lowered 'more rapidly than the sustaining voltage of the other tubes, said particular tube remains ionized under the application of the ionizing voltage `through the common impedance element, whereas the remaining tubes become extinguished after one or more cycles of the alternating voltage because the voltage drop across said impedance element has reduced the voltage applied to their starting gaps below the sustaining value. Therefore, current from the alternating source ows in the main gap of the particular tube as long as the starting gap remains ionized, and all other tubes are ineective since they are locked out by the reduced voltage caused by the common impedance element. b

A feature of the invention is a selecting system of the kind above described in which both electrodes forming the start gap of each tube are connected in direct multiple relation with the corresponding electrodes of all other tubes of the group. By this means of multipling both elec trodes of all tubes the full effect of the voltage drop in the common impedance element is realized, land a greater assurance is given against the possible operation of two tubes simultaneously.

Other features and advantages of the invention will be described more fully in the followtion of group relays in a line ing detailed specification.

In the drawing accompanying the specication:

Fig. 1 shows the invention applied to the selecswitching system; and

Fig. 2 illustrates the invention applied to the selection of the operating magnets of a crossbar switch.

Although the invention is applicable to selectlng and controlling systems in general and without regard to the specific purposes for which these systems are used, it is disclosed in the drawings in connection with line switches of the cross- `bar type when employed in telephone systems. These crossbar line switches serve to extend calling subscribers' lines to idle trunks. and the .con-

the initial trolling circuits therefor usually include horizontal and vertical group relays which determine the order of sequence in which calling lines are served. Fig. 1 shows a portion of the control circuits for one of these switches andillustrates a number ofthe horizontal group relays to which the selective and lock-out features of this invention are applied. Fig. 2 shows the application of the selection and lock-out features of the invention to the select magnets of `one of the crossbar line switches.

A crossbar switch of the type to which reference is here made is disclosed in the patent to Reynolds 2,021,329 of November 19, 1935. l'I'he controlling and operating circuits of these switches, when used as line switches in an automatic telephone system, aredisclosed and de` scribed in detail in the patent to Busch et al. 2,224,251 of December 10, 1940.-

The subscribers lines, which appear inV one of these line switches, are divided into a plurality of groups. Two of these groups of lines and |0| are shown in Fig. l of the drawing, each of the lines |02, |03, |04, |05, feto., being provided with an individual line relay |06, |01, |08, |09, etc. A plurality of group relays ||0, etc., are also provided, there being one of these relays for each group of lines |00, |0|. The usual practice is to divide the total number of lines into ten groups, in which case there would be ten group relays.

Since the calls areinitiated at random on the lines of the several groups and since it is essential that only one of the group relays should operate at a time, it is necessary to provide some means for selecting a particular one of the relays for operation and to prevent the operation of all other relays pertaining to groups having simultaneous calls therein. This exclusive selection is accomplished by means of a series of space discharge tubes, each tube ||2, ||3 of the series being associated with and individual to a corresponding one of the group relays' ||0,

The windings of the group relays are connected respectively to the anodes of the tubes so that the relay obtains its operating current in the main discharge circuit of the tube. For example, fthe windings of relays ||0 and are connected respectively to the anodes ||4 and ||5 of tubes ||2 and ||3. The other terminals of the relays are multipled by a common conductor ||6 which in vturn is connected over conductor |1 to a source of alternating or pulsating current. The cathodes of all tubes of the group, including the cathodes ||8 and ||9 of tubes ||2 and ||3, are connected in direct multiple relation by means of the common multiple conductor |20, which in turn is connected directly to ground. The starting electrode of each tube is connected through contacts of the line relays of the corresponding group to a common supply circuit for applying starting voltage to the control gap of the tube. For example, the starting electrode |2| of tube ||2 is connected in multiple to the front contacts of all line relays |06, |01 in the associated group, and the armatures of these relays are connected in multiple over conductor |22 to the common branch |21 of the supply circuit, which includes battery |23 and resistor I 26. In like manner the starting anode |24 of tube i3 is connected through the front contacts of relays |08 and |09 and multiple conductor |25 over the common branch |21 of the supply circuit to battery |23.

The individual branches |22, |25, etc., of the voltage supply circuit include 4fuses |28, |29 for protecting the respective tubes. The common branch |21 of the supply circuit also includes a variable resistor |30 the purpose of vwhich is to increase the current flow in any one of the individual branches sufficiently to melt the fuse thereof in case the branch becomes accidentally connected directly to ground.

The anode supply circuit |'|1 is connected to a rectifier |3| which serves to rectify the alternatingvoltage furnished by the generator |32. The rectified voltage is thus applied to the supply conductor ||1 in the form of pulsations of positive potential.

'I'he manner in which selection and lock-out are effected in the circuits shown in Fig. 1 will now be explained in detail. Assume that line |02 in the group |00 and line |04 in the group Ill initiate calls at substantially the same time. In response to these calls the corresponding line relays |06 and |00 operate. When relay |06 closes its contacts, a circuit is completed for the application of starting voltage to the control gap of the associated tube ||2. This circuit may be traced from the positive pole of battery |23, resistoxfl, resistor |30, fuse |28, conductor |22, contactsI of relay |06, starting electrode |2|, cathode/H0 to the grounded conductor |20. The voltage thus applied across the control gap |2|||8 causes this gap to lonize.- The resistor |33 which is connected across the control gap is high in value and does not effectively shunt the gap. At the same time the call on line |04 causes the operation of relay |08,and\a-starting circuit for the tube H3 is closed from battery |23, resistor"|2l6, resistor |30 through the fuse |29, conductor |25;-contacts of relay |08, starting electrode |24, cathode I! to the grounded conductor |20. The voltage applied to the control gap |24||9 causes the ionization thereof. Y,

Thus the starting gaps of tubes "I i2 and Hl may commence to ionize at substantially the same instant, and the same might bek true of other tubes corresponding to groups having lines in a calling condition at this time. If these tubes were permitted to continue their ionization and to transfer the ionization from the control gaps to the main gaps at the same time, the result would be that a plurality of group relays ||0, would energize simultaneously and cause a false operation of the system. This false operation, however, is obviated in the present systemf'by using pulsating or alternating voltage on the anodes of the tubes instead of the usual direct voltage source. I have found that when an alternating or pulsating voltage is applied to the anodes of the tubes the sustaining characteristic of the starting gaps of a plurality of tubes undergoes a change which varies substantially among the diiferent tubes. More specifically the voltage across the control gap which is sumcient to sustain ionization is automatically decreased in response to the increasing potential on the anode of the tube resulting from the application of the alternating or pulsating voltage tovthe anode-cathode gap. As the sustaining voltage of the control gap of a particular tube decreases, it is possible to lower correspondingly the voltage applied by the supply circuit Without causing the quenching of the control gapL/provided that the supply voltage remains somewhat greater than the minimum sustaining voltage. This decrease in the sustaining voltage of the control gap in response to the increasing anode potential occurs in each of the several tubes which have ionized their control gaps simultaneously. However, I have, as above mentioned,

found. by numerous experiments that in any given series of tubes the rate of change of the sustaining voltage of any one tube differs from that of the others. Therefore, although two or more tubes may commence theirL ionization at the same instant, one of these will have its control gap sustaining voltage lowered more rapidly than the others when the anode of the tube rises in positive potential in response to the next application of a positive alternation or a positive impulse. Consequently the current flowing through the common resistor |26 and through the control gap of the preferred tube and also in parallel through the control gaps of the other simultaneously ionized tubes produces a voltage drop which lowers the potential of the starting anodes |2I, |24, etc., of' all of the non-preferred tubes below their sustaining voltages. T he result is that the preferred tube continues its ionization, whereas the remaining tubes, either in the first positive cycl or in an immediately succeeding positive cycle of the anode voltage, quench their control gaps and thus become inoperative.

Returning, for example, to the two tubes H2 and H3, assume that the simultaneous ionization of the control gaps of these tubes occurs at an instant when no potential is being applied to'. the anodes H4 and I |5. A moment later positive f potential is applied to these anodes, and the value of this potential continues to rise until it reaches the maximum. As the anode potential rises the voltage necessary to sustain ionization across the control gap in each tube decreases. Since, ho'wever, the rate of decrease of the sustaining voltage differs for the two tubes H2 and I|3, it may be assumed that the sustaining voltage of the tube H2 decreases at a faster rate than that of the tube H3. As the tube H2 lowers its sustaining voltage it draws more and more current from the common supply circuit |21, and the discharge current flowing from the battery |23 through the common resistor |28 lowers the positive potential of the starting electrodes |2I', |23 of all tubes in the group. This lowered potential results in a reduced applied voltage acrossthe starting gap |2||||3, Abut the reduction still does not lower the applied voltage below the sustaining voltage of the gap. Therefore, the tube II 2 continues to maintain the ionization of its control gap. The control gap |24-II9 of the other tube H3 fails to maintain its energization since the applied voltage from the common supply circuit |21 is reduced more rapidly than the sustaining voltage of the gap. And the same would be true of any other tubes that may simultaneously ionize their gaps.

Thus at some point in the rise of the anode voltage ythe ionization of tube H2 transfers from the control gap |2|I I8 to the main gap ||4| I8, and current flows over the supply circuit H1 through the winding of group relay H0, anode I I4, cathode H8 to the grounded circuit |20. The control gap |2I-H8 remains ionized constantly under control of the line relay |06, and current flows in the main gap of. the tube through the relay H0 on each positive alternation or positive impulse from the supply conduc' tor |I'|. -The relay H0 operates in this circuit and remains operated during the brief lintervals of current cessation by reason of its slow-releasing character. After the relay I l0 has performed its functions and it is desired to release the same, the circuit of line relay |06 is opened, or the circuit of the control gap |2I-I I8 is opened at any other convenient point. The opening of the circult for this control gap terminates the ionization thereof, and the main gap of the tube fails to ionize on succeeding alternations of the anode potential. After a brief interval the'relay'IIO releases.

It will be noted that the full benefit of the voltage drop produced across the resistor |26 in the common branch of the circuit extending to the starting electrodes of the tubes is realized by connecting all of the starting electrodes I2|, |24 directly in multiplevto the common branch conductor |21 and on the other hand -by connecting the cathodes H8, H9 of all tubes directly in multiple to the conductor |20, which in turn is connected to ground or to the-negatlve pole of the battery |23.

Althoughthe rectifier |3|, comprising transformer I 3 4 and rectifying elements |35 and |36, is used to convert the alternating voltage from the source |32 into positive pulsations, it will be understood that this rectifier may be omitted and-the alternating voltage applied from the source |32 directly to the common conductor H6.

The resistor |30 is one having a non-linear voltage resistance characteristic. 'Ihe resistance of this unit is relatively high under normal operating conditions and in combination with resistor |26 limits the starting current to the desired value. However, should one of the conductors |22, |25 become grounded by inadver-tence, the increased voltage applied across the resistor |30 decreases its resistance to such an extent that the increased current flowing through the corresponding one of the fuses |28, |29 causes it to melt.

In Fig. 2 a Crossbar switch is partially illustrated for connecting incoming lines, such as the line 200, to outgoing lines or trunks 20|, 202, ete. The horizontal orselect bars of the switch are operated by means of individual select magnets 203, 204, etc., there being one of these select magnets for each of the outgoing circuits 20|, 202. i

In order that the select magnets, which are subject to random selection, may be operated one at a time, the individual discharge tubes 205, 206. etc., are provided for effecting the exclusion or lock-out of all magnets except the one chosen for operation. As in Fig. l, thc anodes 2|0, 2H of the tubes are connected respectively to the windings of the select magnets, and the other terminals of these windings are joined by the common multiple conductor 201 and connected to the alternating potential source 208 which in turn is connected in series to the negative pole of battery 209. The battery 209 applies a negative potential to the anodes of the tubes to balance the negative potential applied to the cathodes by the battery 2|5. This permits the voltage across the main gap of an operated tube to fall to zero each time the alternating current source 208 passes through zero and prevents an operated tube from remaining locked after the control gap ionization ceases. The cathodes 2I2, 2| 3 are all connected directly in multiple to the common conductor 2 I4 and thence to the negaiivc pole of battery 2I5.

The lock-out tubes 205, 206 diller from those shown in Fig. 1 in that they are provided with separate or insulated control gaps. For example, the control gap of tube 205 is formed by a startingr anode 2I6 and a starting cathode 2I1. Likewise the control gap of tube 206 is formed by a starting anode 2|8 and a starting cathode 2I9. The starting cathodes 2 |`I and 2|9 are connected respectively thro lf'resistors 220 and 22| to the negative pole of `battery 222 and battery 223. These starting cathodes are also connected respectively to the sieeve conductors 221 and 225 of the outgoing circuits 20| and 202. The starting anodes ZIE, 2|8etc., are connected directly in multiple by the common conductor 220, which includes in circuit therewith the common resistor 221 and the supply battery 228.

'I'he operation of the selection circuit shown in Fig. 2 will now be described. Assume that it is desired to eieclthe-selection of any one of a plurality of idle outgoing circuits 20|,l 202, etc., for the purposepf extending the .line 200.to..such idle circuit. Inasmuch as a number of these outgoing circuits may be idle at the time, it is necessary that only one be selected, and it does not matter which one, and that all other idle outgoing circuits be positively excluded to avoid, the possibility of a double connection.

When the time arrives for making the selection, a relay 229 is operated in any suitable manner tof/close a circuit from the positive pole of battery 220 through the common resistance 221, contacts of said relay, thence to the starting anodes 2I6, 2IB of all tubes in the group. Each tube corresponding to an idle outgoing'circuit 20|, 202 will have full negativemdtential applied to the starting cathode thereof from the batteries 222, 223. Assume, for" example, that both circuits 20| and 20Lare idle at the moment; the starting gaps of both tubes 205 and 206 ionize, therefore, when the relay /229 is operated. If at this moment the source 208is of the proper polarity, the ionization of the starting gap 2I6--2I1 transfers to the auxiliary starting gap`2rI2-2I6. The circuit for maintaining ionization of theauxiliary gap may be traced over conductor 226, starting anode 2I6, main cathode 2I2, conductor 2I4itofthenegative pole of battery 2I5, Similarly, the ionization of the starting gap 2I8-2 I9 of tube 206 may transfer at the same, time to the auxiliary starting gap 2I3-2I8. As-soonthereafter as the,k source 208 becomes positive, an increasing positive potential is applied to the anodes 2I0, 2| I, and this increasing positive potential changes the sustaining characteristics of the starting gaps of the tubes at different rates as hereinbefore explained. Consequently, the ionization of the starting gap of one of thc tubes is maintained while the starting gap of the remaining tubes is quenched by the voltage drop produced across the common resistor 221 in the starting gap circuit. If it is assumed that the tube 205 changes its sustaining voltage more rapidly vthan the others, then the starting gap 2I2-2I6 of this tube maintains its ionization and the other tubes are quenched. Consequently, the tube 205 transfers the ionization of the'starting gap to the main discharge gap 2| 0-2I2, and current of positive polarity flows from the source 208 through the winding of magnet 203, anode 2I0, cathode 2I2 to the negative pole of battery 2 I5 and thence to ground. The magnet 203 causes the operation of the crossbar switch and the extension of the line circuit 200 to the selected idle outgoing circuit 20|. 'I'he purpose of the rectifying unit 230 is to prevent the magnet 203 fromreleasing during sucessive alternations of the source`208.

As soon as the circuit'20| is seized, a ground potential is applied to the sleeve conductor 22B in any suitable manner to render the control gap 2|62I1 ineiective, so that this circuit will not beselected when a subsequent connection is being established to an idle one of the outgoing cir-y ganadora cuits. At some convenient time in the operation or the system the relay 229` is released to quench the ionized control gaps of alltubes.

While the space discharge.k tubes illustrated herein may be of any suitable type, such as those iilled with different gases, it has been found that better results are obtained in the systems disclosed when tubes lled with argon are employed.

What is claimed is:

1. In combination, a plurality of discharge tubes each having electrodes forming a starting gap and a main discharge gap, a common circuit for applying at randomy a starting voltage t-o cause the ionization of the starting gap ofone or more of said tubes, a source of alternating voltage applied to the main gaps of all of said tubes and serving to alter at different rates the sustaining characteristics of the starting gaps of any tubes that happen to ionize simultaneously, and an impedance element in said common circuit for producing a voltage drop in response to the current owing in the starting gaps of i said tubes, the voltage drop of said impedance element serving to lower below the sustaining value the voltage applied to the starting gaps of all tubes except the particular tube that has its sustaining characteristic altered most rapidly by said alternating voltage.

2. In combination, a plurality of discharge tubes each having electrodes forming a starting gap and a main discharge gap, a common cir'- cuit for applying at random a starting voltage to cause the ionization of -the starting gaps o! a plurality of said tubes simultaneously, a source of alternating voltage applied to the main gaps of all of said tubes and serving to lower at different rates the sustaining voltage of the starting gaps of said tubes, and a resistance element in said common circuit for producing a voltage drop in response to the current owing in the f starting gaps of the ionized tubes, the voltage drop of said resistance element serving to lower below the sustaining value the voltage applied to the starting gaps of all tubes except the particular tube-that has its sustaining voltage lowered most rapidly by said alternating voltage.

3. In combination, a plurality of discharge tubes each having two starting electrodes forming a starting gap and a, main electrode forming a main gap with one of said starting electrodes. a common circuit including in multiple relation one of the starting electrodes of each of said tubes, a common circuit including in multiple relation the other starting electrodes of each of said tubes, means for applying at random over said common multiple circuits a starting voltage to cause the ionization of the starting gaps of a plurality of said tubes simultaneously, a source of voltage applied to the main gaps of all of said tubes and serving to alter at different rates the sustaining characteristics of the starting gaps of the simultaneously ionized tubes, and an impedance element in one of said common circuits for producing a voltage drop in response to the current owing in the starting gaps vof said tubes, the voltage drop of said impedance element serving to lower below the sustaining value the voltage applied to the starting gaps of all tubes except the particular tube that has its sustaining voltage lowered at the highest rate.

4. In combination, a plurality of discharge tubes each having electrodes forming a starting gap and a main discharge gap, a circuit for the starting gaps of said tubes including a common branch and an individual branch for each tube.

means for closing said individual branches at random to apply a starting voltage toY cause the ionization or the starting gap of the corresponding tube, a source of alternating voltage applied to the main gaps of all of said tubes and serving to alterat different rates the sustaining voltage of the starting gaps of any two or more of the simultaneously ionized tubes, an impedance element in `saidl common branch foi-'producing a voltage dropin response to the current owlng in theistarting gaps of said tubesthe voltage 10 mains closed.

NATHAN I. HALL. 

